1. Field of the Invention
The present invention relates to a method of dry-etching semiconductor devices, and more particularly, to a method of dry-etching using a photoresist suitable for ArF as an etching mask.
2. Description of the Related Art
Material layers having a variety of electrical characteristics, such as, for example, conductive layers, semiconductor layers, and insulating layers, are formed on a semiconductor substrate. Next, the material layers are each patterned according to predesigned circuits. As a result, semiconductor integrated circuits are manufactured.
The patterning of the material layers is performed by a photolithography process. In other words, a photoresist layer, which later undergoes a photochemical reaction, is formed on particular material layers to be patterned. Next, a photo mask or a reticle in which a transfer image is already formed is positioned on a semiconductor substrate on which the photoresist layer is formed. When the photoresist layer is exposed to light having a particular wavelength, a photochemical reaction occurs at particular portions of the photoresist layer. Next, portions at which a photochemical reaction occurs or does not are removed, according to the kind of photoresist used with a developer, to thereby form photoresist patterns. The particular material layers are etched and patterned using the photoresist patterns as an etching mask. The photolithography process becomes more important as the design rule is reduced in the trend toward higher integration semiconductor integrated circuits.
Photoresist suitable for KrF, which is supplied using a KrF excimer laser having an exposure wavelength of 248 nm as an exposure light source, is used in a photolithography process for forming patterns of 0.18 μm according to a design rule. When the design rule in a photolithography process results in forming patterns of 0.13 μm according to the high integration density of semiconductor devices, the size of patterns is about half of the KrF wavelength. Thus, preferred pattern profiles can not be secured due to a limit in resolution on patterns having a size equal to or smaller than about half of a KrF wavelength. Therefore, a photolithography process for forming patterns of 0.13 μm inevitably uses a combination of a KrF technique and an ultraresolution technique such as a half-tone illumination technique, a phase shift mask (“PSM”) technique, and an optical proximity correction (“OPC”) technique.
The KrF-based technique used with the ultraresolution technique is applied up to a line width of 0.11 μm, but reaches its limit in a line width of 0.10 μm due to a sharp increase in the time required for manufacturing mask patterns and an increase in the development costs. Thus, an ArF excimer laser having an exposure wavelength of 193 nm is introduced to an exposure technique.
However, the ArF technique has the following problems. First, when a photolithography process is performed using photoresist suitable for ArF, a light source having a short wavelength of 193 nm is used in an exposure equipment to increase resolution. Here, the light source with the short wavelength has poor transmissivity with respect to photoresist and thus thins the thickness of the photoresist.
Second, photoresist suitable for ArF has lower carbon content and higher oxygen content than photoresist suitable for KrF. Thus, the resistance of a photoresist suitable for ArF to dry-etching is remarkably reduced compared to a photoresist suitable for KrF.
Third, in a KrF-suitable photoresist process, an inorganic anti-reflective layer having an excellent adhesion to the KrF-suitable photoresist is used as an anti-reflective layer whereas an organic anti-reflective layer is used as anti-reflective layer in an ArF-suitable photoresist process. However, since an organic anti-reflective layer is formed of a hydrocarbon polymer similar to the photoresist, it is very difficult to maintain high etch selectivity during dry-etching. Thus, the ArF-suitable photoresist process requires much higher photoresist selectivity, i.e., higher resistance to dry-etching, than the KrF-suitable photoresist during dry-etching.
Accordingly, if materials to be etched are etched by a general dry-etching method using an ArF-suitable photoresist, patterns becomes wiggled (so-called “wiggling phenomenon”), or upper portions or sides of patterns are striated (so-called “striaton phenomenon”), or patterns are fallen down due to the lack of resistance of the ArF-suitable photoresist to dry-etching. As a result, it is difficult to form the desired patterns. In particular, if ArF-suitable photoresist patterns are used in a process using silicon nitride having a thickness of about 2,000 Å as a hard mask formed on gate lines or bit lines of semiconductor DRAMs, this problem becomes more serious.
Therefore, the development of a new etching method is required in order to form the desired patterns in an ArF process introduced to cope with a reduction in the design rule accompanying the high integration density of semiconductor devices.